The present invention relates generally to liquid crystal display devices, and more particularly to a telecentric helmet mounted display for use in a liquid crystal display source.
In order to use rectilinear solid state image sources without distortion correction, an on-axis helmet mounted display optical system is commonly required. This may be accomplished using a number of conventional optical schemes. However, these conventional optical systems have a problem relating to significantly reduced see-through and brightness. For example, a beamsplitter may be added in the optical path between a wearer's eye and a visor/combiner of the helmet mounted display, to keep axial rays on-axis. However, this system is at least five times dimmer than an off-axis version of the same system. Furthermore, the amount of available eye relief is cut in half compared with the off-axis version. In addition, manufacturers of helmet mounted displays such as Kaiser, Honeywell, and GEC have demonstrated on-axis systems that use cathode ray tubes as image sources, but all of them suffer from the above-described on-axis problems.
It is conceivable that other optical measures may be employed to correct for distortion, such as employing a plurality of off-axis relays in the helmet mounted display. However, this approach would significantly increase the weight of the helmet mounted display.
In order to overcome the above-mentioned problems, the assignee of the present invention is developing "anamorphic" fiber optic devices that directly correct distortion in a helmet mounted display. However, helmet mounted displays using this device may have a cost and weight penalty that might limit their use in commercial products.
It is therefore an objective of the present invention to provide for a helmet mounted display having an improved display source that overcomes the limitations of conventional systems described above.